A variety of exothermic materials have so far been proposed. For example, Japanese Patent Publication Kokai No. 61(1986)-55,168 proposes heat-resistant conductive paints containing, as a major ingredient, graphite covered with nickel; Japanese Patent Publication Kokai No. 64(1989)-680 proposes a conductive and exothermic paste containing a metal oxide as a major ingredient; Japanese Patent Publication Kokai No. 1(1989)-108,276 proposes conductive and exothermic paints containing spherical carbon particles as a major component. These exothermic materials, however, have relatively high electrical resistance and they cannot provide a sufficient magnitude of electric current, so that they cannot generate a high calorific value. Hence, in order to provide a high calorific value, a density of electric current should be enhanced by shortening a distance between electrodes or by applying high voltage.
Further, Japanese Patent Publication Kokai No. 1(1989)-108,276 discloses conductive and exothermic paints containing as major ingredients carbon particles and a synthetic resin, carbon particles containing approximately 60% or larger than 60% of spherical particles having a particle size of 500 microns or smaller. This publication, however, describes to the effect that conventional exothermic paints comprising carbon particles in the form of flakes, needles, fiber or shells cannot provide a wide exothermic surface having no local heat spots and a uniform distribution of temperatures.